A carboxylic acid such as succinic acid or its derivative is widely used as a material for a polymer such as a polyester or a polyamide, particularly as a material for a biodegradable polyester, or as a material for food products, pharmaceuticals and cosmetics. Further, a tricarboxylic acid such as citric acid is widely used as a food additive, etc. In recent years, particularly succinic acid is expected to be a material for a biodegradable polymer, together with lactic acid.
Succinic acid has heretofore been industrially obtained by hydrogenation of maleic acid, and the maleic acid is a material derived from petroleum. Accordingly, as a technique to produce an organic acid such as succinic acid, malic acid, tartaric acid or citric acid from a material derived from a plant, a technique to utilize a fermentation operation has been studied. Further, an amino acid has already been produced by a fermentation method, but separation and purification of an amino acid have been carried out usually by isoelectric point precipitation employing sulfuric acid.
Further, such an organic acid as a dicarboxylic acid or a tricarboxylic acid has at least two carboxyl groups, or carboxyl groups and an amino group, as functional groups. Due to such hydrogen bonds, its melting point is usually high (usually at least 120° C.), and in its production process, a distillation operation as a common separation/purification method, can not be employed. Further, in the production of such an organic acid by fermentation, neutralization is usually required, since a microorganism such as fungus or mold to be used for the fermentation does not show an adequate activity usually under a low pH condition. Accordingly, an organic acid obtainable from a fermenter, is usually in the form of a salt with an alkali used for the neutralization. This is a factor which makes the separation/purification of such an organic acid more difficult.
Heretofore, a method employing electrodialysis (JP-A-2-283289) is available as a common separation/purification method for a salt of an organic acid formed by fermentation. However, the electrodialysis has a problem that since the apparatus is large in proportion to production scale, and the scale merit is small even by production on an industrial scale, and consequently the cost tends to be high.
Further, a method of employing an ion exchange resin has been proposed (U.S. Pat. No. 6,284,904). However, in this method, a salt of a strong acid and strong base (such as NaCl) will be formed at the time of regenerating the ion exchange resin, and eventually, this salt is required to be disposed or to be treated by electrodialysis.
Further, a method of decomposing calcium succinate with sulfuric acid has been proposed (JP-A-3-030685). However, in this method, calcium sulfate will be formed in a large amount as a byproduct, and its treatment is problematic.
Further, as an effective method, a method of carrying out reactive crystallization by an exchange reaction of a salt by means of sulfuric acid has been proposed (JP-A-2001-514900, U.S. Pat. No. 5,958,744). Namely, this is a method for precipitating and separating an organic acid by carrying out reactive crystallization by adding sulfuric acid to an ammonium salt of an organic acid.
In this method, a soluble amount of the ammonium salt of the organic acid will remain in the crystallization mother liquor after separating the organic acid by crystallization, and ammonium sulfate will also be contained in this crystallization mother liquor. In order to increase the recovery rate of the entire process, it is necessary to recover such an ammonium salt of the organic acid remaining in the crystallization mother liquor, but even if a crystallization operation is further applied to this crystallization mother liquor, it is extremely difficult to separate ammonium sulfate in solid form, while permitting the ammonium salt of the organic acid to remain in the liquid. Otherwise, even if it is attempted to carry out separation by a gas/liquid separation operation such as distillation, the ammonium salt of the organic acid and ammonium sulfate have very high melting points, and under such a high temperature condition as to vaporize these compounds, the ammonium salt of the organic acid will undergo a dehydration reaction, and it would be impossible to recover the organic acid. Further, by this method, a special installation has been required to carry out pyrolysis of ammonium sulfate at a temperature of at least 300° C. in order to recover and reuse sulfuric acid from ammonium sulfate.
It is an object of the present invention to solve such conventional problems and to provide a novel method for producing organic acid A having a high purity by separating and purifying free organic acid A from a salt of organic acid A formed by a fermentation method by bioconversion of a carbon source in the presence of a neutralizing agent.
Another object of the present invention is to provide a method for producing organic acid A efficiently at a low cost with a low level of waste in consideration of environment, by decomposing and reusing a byproduct salt formed in the above-mentioned novel method for producing organic acid A.